Upper respiratory tract infections (URIs) are a significant health burden in childhood. The average child suffers 6-8 URIs per year, and up to one-third of these are complicated by secondary bacterial infections. We previously conducted a study to assess the efficacy of Echinacea as a treatment for acute URIs in children. Unfortunately, the results of this study indicate that Echinacea was not significantly superior to placebo in treating URI symptoms in patients 2-11 years old. However, a surprising finding of the project was that children who received Echinacea had fewer subsequent URI than placebo recipients. The proposed project is designed to ascertain if Echinacea is effective in preventing URIs in healthy children, 2-11 years old, and to assess the efficacy and safety of two dosing regimens. Study patients will be randomized to receive standard dose Echinacea 10 days/month for 3 months, high dose Echinacea 10 days/month for three months, or placebo. Respiratory specimens from 100 randomly selected study children with clinical URIs will be assayed for detection of common viral pathogens. Biologic activity of the Echinacea product used in the study will be validated by quantifying increased macrophage activation in vitro. The main study outcomes will be number of clinical URIs during a 120-day observation period, and adverse events. It is postulated the that patients receiving one or more of the Echinacea treatment regimens will have significantly fewer URIs than placebo recipients, and that the use of Echinacea will not lead to significant adverse events. For the proposed project it is anticipated that 660 patients will be enrolled over a 42-month study period.